Methods for automated application of hardfacing material to drill bits

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 12/257,219, filed Oct. 23, 2008, now U.S. Pat. No. 8,450,637, issued May 28, 2013, the disclosure of which is incorporated herein in its entirety by this reference. The subject matter of this application is related to the subject matter of U.S. patent application Ser. No. 12/341,595, filed Dec. 22, 2008; U.S. patent application Ser. No. 12/603,734, filed Oct. 22, 2009, which claims the benefit of U.S. Provisional Patent Application Ser. No. 61/109,427, filed Oct. 29, 2008; U.S. patent application Ser. No. 12/562,797, filed Sep. 18, 2009, now U.S. Pat. No. 8,698,038, issued Apr. 15, 2014; and U.S. patent application Ser. No. 12/651,113, filed Dec. 31, 2009, now U.S. Pat. No. 8,471,182, issued Jun. 25, 2013; the disclosure of each of which is incorporated herein in its entirety by this reference.

FIELD

The present invention relates to a system and method for the application of hardfacing to portions of a drill bit using robotic apparatus.

BACKGROUND

In the exploration of oil, gas, and geothermal energy, wells or boreholes in the earth are created in drilling operations using various types of drill bits. These operations typically employ rotary and percussion drilling techniques. In rotary drilling, the borehole is created by rotating a drill string having a drill bit secured to its lower end. As the drill bit drills the well bore, segments of drill pipe are added to the top of the drill string. While drilling, a drilling fluid is continually pumped into the drilling string from surface pumping equipment. The drilling fluid is transported through the center of the hollow drill string and through the drill bit. The drilling fluid exits the drill bit through one or more nozzles in the drill bit. The drilling fluid then returns to the surface by traveling up the annular space between the well bore and the outside of the drill string. The drilling fluid transports cuttings out of the well bore as well as cooling and lubricating the drill bit.

The type of drill bit used to drill the well will depend largely on the hardness of the formation being drilled. One type of rotary rock drill is a drag bit. Early designs for a drag bit included hardfacing applied to various portions of the bit. Currently, designs for drag bits have extremely hard cutting elements, such as natural or synthetic diamonds, mounted to a bit body. As the drag bit is rotated, the cutting elements the bottom and sides of the well bore.

Another typical type of rotary drill bit is the tri-cone roller drill bit that has roller cones mounted on the body of the drill bit, which rotate as the drill bit is rotated. Cutting elements, or teeth, protrude from the roller cones. The angles at which the roller cones are mounted on the bit body determine the amount of “cut,” or “bite” of the bit with respect to the well bore. As the roller cones of the drill bit roll on the bottom of the hole being drilled, the teeth or carbide inserts apply a high compressive and shear loading to the formation causing fracturing of the formation into debris. The cutting action of roller cones comprises a combination of crushing, chipping and scraping. The cuttings from a roller cone drill bit typically comprise a mixture of chips and fine particles.

Yet another type of rotary drill bit is a hybrid drill bit that has a combination of hard cutting elements, such as natural or synthetic diamonds and roller cones mounted on the body of the drill bit.

There are two general types of roller cone drill bits; TCI bits and steel-tooth bits. “TCI” is an abbreviation for Tungsten Carbide Insert. TCI roller cone drill bits have roller cones having a plurality of tungsten carbide or similar inserts of high hardness that protrude from the surface of the roller cone. Numerous styles of TCI drill bits are designed for various types of formations, in which the shape, number and protrusion of the tungsten carbide inserts on the roller cones of the drill bit will vary, along with roller cone angles on the drill bit.

Steel-tooth roller cone drill bits are also referred to as milled-tooth bits because the steel teeth of the roller cones are formed by a milling machine. However, in larger bits, it is also known to cast the steel teeth and, therefore, “steel-tooth” is a better reference. A steel-tooth roller cone drill bit uses roller cones, with each cone having an integral body of hardened steel with teeth formed on the periphery. There are numerous styles of steel-tooth roller cone drill bits designed for formations of varying hardness in which the shape, number and protrusion of the teeth will vary, along with roller cone angles on the drill bit.

The cost efficiency of a drill bit is determined by the drilling life of the drill bit and the rate at which the drill bit penetrates the earth. Under normal drilling conditions, the teeth of the steel-tooth roller cone drill bits are subject to continuous impact and wear because of their engagement with the rock being drilled. As the teeth are worn away, the penetration rate of the drill bit decreases causing the cost of drilling to increase.

To increase the cost efficiency of a steel-tooth roller cone drill bit or a hybrid drill bit having steel-tooth roller cones, it is necessary to increase the wear resistance of the steel teeth. To accomplish this, it is known to deposit one or more layers of a wear-resistant material or “hardfacing” to the exposed surfaces of the steel teeth. Fusion hardfacing refers to a group of techniques that apply (fuse) a wear-resistant alloy (hardfacing) to a substrate metal. Common hardfacing techniques include arc welding and gas torch welding, among other welding processes.

Conventional welding techniques used to apply hardfacing to steel-tooth roller cone drill bits include oxyacetylene welding (OAW) and atomic hydrogen welding (AHW). Currently, manual welding is typically used in the commercial production of roller cone rock bits. Roller cones are mounted on a positioning table while a welding torch and welding rod are used to manually apply hardfacing to portions of each tooth of each roller cone by a welder moving from tooth to tooth and cone to cone from various positions.

Conventional hardfacing materials used to add wear resistance to the steel teeth of a roller cone drill bit include tungsten carbide particles in a metal matrix, typically cobalt or a mixture of cobalt and other similar metals. Many different compositions of hardfacing material have been employed in the rock bit field to achieve wear-resistance, durability and ease of application. Typically, these hardfacing materials are supplied in the form of a welding rod, but can be found in powder form for use with other types of torches.

The physical indicators for the quality of a hardfacing application include uniformity, thickness, coverage, porosity, and other metallurgical properties. Typically, the skill of the individual applying hardfacing determines the quality of the hardfacing. The quality of hardfacing varies between drill bits as well as between the roller cones of a drill bit, and individual teeth of a roller cone. Limited availability of qualified welders has aggravated the problem because the application of hardfacing is extremely tedious, repetitive, skill-dependent, time-consuming, and expensive. The application of hardfacing to roller cones is considered the most tedious and skill-dependent operation in the manufacture of a steel-toothed roller cone drill bit. The consistency of the application of hardfacing to a drill bit by a skilled welder varies over different portions of the drill bit.

To summarize, manually applying hardfacing to a roller cone involves the continuous angular manipulation of a torch over the roller cone, the roller cone held substantially stationary, but being rotated on a positioning table. After hardfacing is manually applied to a surface of each tooth of the roller cone using a torch and welding rod containing the hardfacing material, the positioning table and cutter are indexed to a new angle and position to permit application of hardfacing to a surface of the next tooth of the roller cone until all the cutters have been rotated 360 degrees. At that time, the angle of the table and cutter is adjusted for the application of hardfacing to another tooth surface or row of teeth of the roller cone.

When attempts to utilize robotics to automate the welding process were made, the same configuration was used having a robotic to replace the human operator's arm and its varied movements, while leaving the roller cone on a positioning table. The positioning table is capable of automatic indexing between teeth and rows of teeth of a roller cone.

This configuration and procedure would be expected to provide the recognized benefits of manual hardfacing for a number of reasons. First, manual and automatic torches are much lighter and easier to continuously manipulate than the heavy steel cutters with teeth protruding in all directions. Second, the roller cone must be electrically grounded, and this can be done easily through the stationary positioning table. Third, gravity maintains the heavy roller cone in position on the positioning table. Fourth, highly angled (relative to vertical) manipulation of the torch allows access to confined spaces between teeth of the roller cone and is suited to the highly articulated movement of a robotic arm.

U.S. Pat. No. 6,392,190 provides a description of the use of a robotic aim in hardfacing of roller cones, in which the torch is held by a robotic arm and the roller cones are moved on a positioning table. A manual welder is replaced with a robotic aim for holding the torch. The robotic arm and a positioning table are combined to have more than five movable axes in the system for applying hardfacing. However, U.S. Pat. No. 6,392,190 does not describe details of solutions to the numerous obstacles in automating the hardfacing of roller cones using robotic arms and positioners.

One factor limiting use of robotic hardfacing has been the unsatisfactory appearance of the final product when applied using robotically held torches over stationary cutters. Another factor limiting use of robotic hardfacing to rolling cutters is the commercial unavailability of a material that directly compares to conventional Oxygen Acetylene Welding (OAW) welding rod materials that can be applied with commercially available Plasma Transferred Arc (PTA) torches.

Another factor limiting use of robotic hardfacing is the inability to properly identify and locate individual roller cone designs within a robotic hardfacing system. The roller cones of each size of drill bit and style of drill bit are substantially different, and initiating the wrong program could cause a collision of the torch and part, resulting in catastrophic failure and loss. Another factor limiting use of robotic hardfacing is the inability to correct the critical positioning between the torch and roller cone in response to manufacturing variations of the cutter, wear of the torch, and buildup of hardfacing.

Still another factor limiting use of robotic hardfacing has been the inability to properly access many of the areas on the complex surface of a roller cone that require hardfacing with commercially available Plasma Transferred Arc (PTA) torches large enough to permit application of the required material. A small form factor (profile) is required to access the roots of the teeth of a roller cone that are close together. However, most conventional PTA torches require large powder ports to accommodate the flow of the medium-to-large mesh powder required for good wear resistance. Torches with smaller nozzles have smaller powder ports that prohibit proper flow of the desired powders.

Another factor limiting use of robotic hardfacing is the complexity of programming a control system to coordinate the critical paths and application sequences needed to apply the hardfacing. For example, undisclosed in the prior art, the known torch operating parameters, materials, application sequences, and procedures used for decades in manual hardfacing operations have proven to be mostly irrelevant to robotic hardfacing of roller cones. A related factor limiting use of robotic hardfacing is the cost and limitation of resources. A significant investment and commitment of machine time are required to create tests, evaluate results, modify equipment, and incrementally adjust the several operating parameters, and then integrate the variations into production part programs. These and several other obstacles have, until now, limited or prevented any commercial practice of automated hardfacing of roller cones.

Therefore, there is a need to develop a system and method for applying hardfacing to roller cones consistent with the highest material and application quality standards obtainable by manual welding. There is also a need to develop a system that identifies parts, selects the proper program, and provides programmed correction in response to manufacturing variations of the roller cones, wear of the torch, and buildup of hardfacing. There is also a need to develop a PTA torch design capable of accessing more of the areas on a roller cone's cutter that require hardfacing. There is also a need to develop a hardfacing material, the performance of which will compare favorably to conventional Oxygen Acetylene Welding (OAW) materials and flow properly through the PTA torch design.

BRIEF SUMMARY

A system and method for the application of hardfacing to surfaces of drill bits is disclosed.

In some embodiments, methods for depositing hardfacing material on portions of drill bits comprise providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a substantially vertical plane. A rolling cutter is secured to a chuck mounted on an articulated arm of a robot. A surface of a tooth of the rolling cutter is positioned in a substantially perpendicular relationship beneath the torch. The torch is oscillated along a substantially horizontal axis. The rolling cutter is moved with the articulated arm of the robot in a plane beneath the oscillating torch. A hardfacing material is deposited on the tooth of the rolling cutter.

In other embodiments, methods for depositing hardfacing material on portions of drill bits comprise providing a vertically oriented plasma transfer arc torch secured to a positioner having controllable movement in a substantially vertical plane. A cutter is secured to a chuck mounted on an articulated arm of a robot. A surface of a tooth of the cutter is positioned in a substantially perpendicular relationship beneath the torch. A first waveform target path is provided and the torch is oscillated along a substantially horizontal axis. The cutter is moved with the articulated arm of the robot beneath the midpoint of the oscillating torch path so as to impose a second torch waveform onto the first waveform target path to create a hardfacing pattern on a tooth.

In still other embodiments, methods for depositing hardfacing material on the teeth of rolling cutters of rock bits, wherein the rolling cutter has protruding teeth on a plurality of rows, comprise providing a vertically oriented plasma transfer arc torch, secured to a positioner in a substantially vertical plane. The rolling cutter is secured to a chuck mounted on an articulated arm of a robot and a surface of a tooth of the rolling cutter is positioned in a substantially horizontal plane beneath the torch. A bead of hardfacing material is deposited on the tooth of the rolling cutter while moving the rolling cutter with the articulated aim of the robot.

In yet other embodiments, methods for hardfacing portions of drill bits comprise providing a portion of a drill bit having thin and thick portions and providing a plasma transfer arc torch secured to a positioner having program controllable motion. One of a portion of the drill bit and the drill bit is secured to a chuck mounted on an articulated arm of a robot having programmable controlled motion. A weld path is begun at the thin portion of the drill bit and hardfacing is deposited in a path directed towards the thick portion of the drill bit. Torch amperage is increased in proportion to a weld area as the torch path moves towards the thick portion of the drill bit.

In other embodiments, methods for hardfacing rock bits comprise providing a drill bit and providing indexing indicium on the drill bit. A positioning sensor is indexed to the indicium on the drill bit to determine the location of the drill bit. A torch location is calibrated to the drill bit based indexed drill bit location.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The objects and features of the invention will become more readily understood from the following detailed description and appended claims when read in conjunction with the accompanying drawings in which like numerals represent like elements.

The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown as exaggerated or enlarged to facilitate an understanding of the invention.

<figref idref="DRAWINGS">FIG. 1</figref> is a side view of a steel-tooth drill bit.

<figref idref="DRAWINGS">FIG. 1A</figref> is a side elevational view of an earth-boring drill bit according to an embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 1B</figref> is a side elevational view of a drag bit type earth-boring drill bit according to an embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 2</figref> is an isometric view of a typical steel-tooth cutter such as might be used on the steel-tooth drill bit of <figref idref="DRAWINGS">FIG. 1</figref>.

<figref idref="DRAWINGS">FIG. 2A</figref> is a partial sectional view of an embodiment of a rotatable cutter assembly, including a cone, of the present invention that may be used with the earth-boring drill bit shown in <figref idref="DRAWINGS">FIG. 1A</figref>.

<figref idref="DRAWINGS">FIG. 2B</figref> is a sectional view of another embodiment of a rotatable cone of the present invention that may be used with the earth-boring drill bit shown in <figref idref="DRAWINGS">FIG. 1A</figref>.

<figref idref="DRAWINGS">FIG. 3</figref> is an isometric view of a typical steel-tooth such as might be located on the steel-tooth cutter of <figref idref="DRAWINGS">FIG. 2</figref>.

<figref idref="DRAWINGS">FIG. 4</figref> is an isometric view of the steel-tooth of <figref idref="DRAWINGS">FIG. 3</figref> after hardfacing has been applied.

<figref idref="DRAWINGS">FIG. 5</figref> is a schematic of a preferred embodiment of a robotic welding system of the present invention for a cone.

<figref idref="DRAWINGS">FIG. 5A</figref> is a schematic of another embodiment of the robotic welding system of the present invention for a drag type drill bit.

<figref idref="DRAWINGS">FIG. 6</figref> is an isometric view of a robot manipulating a cutter to be hardfaced.

<figref idref="DRAWINGS">FIG. 7</figref> is an isometric view of a cutter positioned beneath a torch in preparation for the application of hardfacing.

<figref idref="DRAWINGS">FIG. 8</figref> is an isometric view of a chuck of a preferred type to be attached to an end of a robot.

<figref idref="DRAWINGS">FIG. 9</figref> is an isometric view of a jaw for a three-jaw chuck specially profiled to include a journal land and a race land for gripping a rolling cutter.

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic side view of a positioner and a torch.

<figref idref="DRAWINGS">FIG. 11</figref> is a schematic cross-section of the torch shown in <figref idref="DRAWINGS">FIG. 10</figref>.

<figref idref="DRAWINGS">FIG. 12</figref> is a cross-section of a torch configured in accordance with a preferred embodiment.

<figref idref="DRAWINGS">FIG. 13</figref> is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to outer ends of the teeth.

<figref idref="DRAWINGS">FIG. 13A</figref> is an isometric view illustrating a robot manipulating a torch and a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the outer ends of the teeth.

<figref idref="DRAWINGS">FIG. 14</figref> is a side view illustrating a torch applying hardfacing to the outer end of a tooth on an outer row of the cutter.

<figref idref="DRAWINGS">FIG. 15</figref> is a side view illustrating the torch applying hardfacing to a leading flank of a tooth on the outer row of the cutter.

<figref idref="DRAWINGS">FIG. 16</figref> is an isometric view illustrating a robot manipulating a rolling cutter into position in preparation of the application of hardfacing to the inner end of a tooth on the cutter.

<figref idref="DRAWINGS">FIG. 17</figref> is a bottom view of a typical steel-tooth such as might be located on the steel-tooth cutter of <figref idref="DRAWINGS">FIG. 2</figref>, illustrating a substantially trapezoidal waveform target path for hardfacing in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 18</figref> is a schematic representation of oscillation of the torch on an axis of an oscillation “AO” having an oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 19</figref> is a schematic representation of a substantially triangular waveform torch path for hardfacing in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 20</figref> is a schematic representation of a waveform created by oscillation of a cutter relative to an intersection of a target path and oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 21</figref> is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of <figref idref="DRAWINGS">FIG. 20</figref>.

<figref idref="DRAWINGS">FIG. 22</figref> is a schematic representation of a generally rectangular shaped waveform created by oscillation of a cutter relative to an intersection of a target path and oscillation midpoint “OM” in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 23</figref> is a schematic representation of a modified waveform of hardfacing created in accordance with the preferred embodiment of <figref idref="DRAWINGS">FIG. 22</figref>.

<figref idref="DRAWINGS">FIG. 24</figref> is a schematic representation of a “shingle” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 25</figref> is a schematic representation of a “herringbone” pattern of hardfacing applied to a tooth of a cutter, in accordance with a preferred embodiment of the present invention.

<figref idref="DRAWINGS">FIG. 26A</figref> is a cross-section of the cone illustrated in <figref idref="DRAWINGS">FIG. 2A</figref> having hardfacing thereon.

<figref idref="DRAWINGS">FIG. 26B</figref> is a cross-section of the cone illustrated in <figref idref="DRAWINGS">FIG. 2B</figref> having hardfacing thereon.

<figref idref="DRAWINGS">FIG. 27</figref> is a side elevational view of a drag type earth-boring drill bit according to an embodiment of the present invention having hardfacing applied to portions thereof.

DETAILED DESCRIPTION

The system and method of the present invention have an opposite configuration and method of operation to that of manual hardfacing and prior automated hardfacing systems. In the present system and method a robotic system is used, having a plasma transfer arc torch secured in a substantially vertical position to a torch positioner in a downward orientation. The torch positioner is program-controllable in a vertical plane. Shielding, plasma, and transport gases are supplied to the torch through electrically controllable flow valves. Rather than use a torch positioner, a robotic arm can be used having a transfer arc torch secured thereto in a substantially vertical position in a downward orientation. For handling a roller cone, a robot having program controllable movement of an articulated arm is used. A chuck adapter is attached to the arm of the robot. A three jaw chuck is attached to the chuck adapter. The chuck is capable of securely holding a roller cone in an inverted position.

A first position sensor is positioned for determining the proximity of the torch to a surface of the roller cone. A second position sensor may be positioned for determining the location, orientation, or identification of the roller cone. A programmable control system is electrically connected to the torch, the torch positioner or robotic arm having the torch mounted thereon, the robot, shielding, plasma, and transport gas flow valves, and the position sensors programmed for operation of each. The robot is programmed to position a surface of a cutter below the torch prior to the application of welding material to the roller cone.

In this configuration, the torch is oscillated in a horizontal path. The roller cone is manipulated such that a programmed target path for each tooth surface is followed beneath the path midpoint (or equivalent indicator) of the oscillating torch. The movement of the roller cone beneath the torch generates a waveform pattern of hardfacing. In a preferred embodiment, the target path is a type of waveform path as well. Imposing the torch waveform onto the target path waveform generates a high-quality and efficient hardfaced coating on the roller cone. In another preferred embodiment, the roller cone is oscillated in relation to the torch as it follows the target path. This embodiment provides the ability to generate unique and desirable hardfacing patterns on the surface of the cutter, while maintaining symmetry and coverage.

An advantage of the system and method of the present invention is that it automates the hardfacing application of roller cones or any other desired portion of a drill bit, which increases the consistency and quality of the applied hardfacing, and thus the reliability, performance, and cost efficiency of the roller cone and the drill bit. Another advantage of the system and method of present invention is that it reduces manufacturing cost and reliance on skilled laborers. Another advantage of the system and method of the present invention is that by decreasing production time, product inventory levels can be reduced. Another advantage of the system and method of the present invention is that it facilitates the automated collection of welding data, from which further process controls and process design improvements can be made.

Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone and a robotic arm having the torch mounted thereon improves the opportunity to integrate sensors for providing feedback. Another advantage of the system and method of the present invention is that utilization of the robotic arm to manipulate the roller cone provides the necessary surface-to-torch angularity for access, without disrupting the flow of the powder due to changes in the angle of the torch.

As referred to hereinabove, the “system and method of the present invention” refers to one or more embodiments of the invention, which may or may not be claimed, and such references are not intended to limit the language of the claims, or to be used to construe the claims. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

<figref idref="DRAWINGS">FIG. 1</figref> is a side view of a steel-tooth roller cone drill bit <b>1</b>. The drill bit <b>1</b> has a plurality of roller cones <b>10</b>. <figref idref="DRAWINGS">FIG. 2</figref> is an isometric view of a typical steel-tooth roller cone <b>10</b> such as might be used on the drill bit of <figref idref="DRAWINGS">FIG. 1</figref>. Steel-tooth roller cone <b>10</b> has a plurality of rows of teeth <b>20</b>. In <figref idref="DRAWINGS">FIG. 2</figref>, roller cone <b>10</b> has an inner row of teeth <b>12</b>, an intermediate row of teeth <b>14</b>, and an outer row of teeth <b>16</b>. Each of rows of teeth <b>12</b>, <b>14</b>, and <b>16</b> has one or more teeth <b>20</b> therein.

<figref idref="DRAWINGS">FIG. 1A</figref> is a side elevational view of an earth-boring drill bit <b>510</b> according to another embodiment of the present invention. The earth-boring drill bit <b>510</b> includes a bit body <b>512</b> and a plurality of rotatable cutter assemblies <b>514</b>. The bit body <b>512</b> may include a plurality of integrally formed bit legs <b>516</b>, and threads <b>518</b> may be formed on the upper end of the bit body <b>512</b> for connection to a drill string (not shown). The bit body <b>512</b> may have nozzles <b>520</b> for discharging drilling fluid into a borehole, which may be returned along with cuttings up to the surface during a drilling operation. Each of the rotatable cutter assemblies <b>514</b> include a cone <b>522</b> comprising a particle-matrix composite material and a plurality of cutting elements, such as the cutting inserts <b>524</b> shown. Each cone <b>522</b> may include a conical gage surface <b>526</b>. Additionally, each cone <b>522</b> may have a unique configuration of cutting inserts <b>524</b> or cutting elements, such that the cones <b>522</b> may rotate in close proximity to one another without mechanical interference.

<figref idref="DRAWINGS">FIG. 1B</figref> illustrates a drill bit <b>610</b> incorporating a plurality of nozzle assemblies <b>630</b> therein. The drill bit <b>610</b> is configured as a fixed-cutter rotary full bore drill bit, also known in the art as a “drag bit.” The drill bit <b>610</b> includes a crown or bit body <b>611</b> composed of steel body or sintered tungsten carbide body coupled to a support <b>619</b>. The support <b>619</b> includes a shank <b>613</b> and a crossover component (not shown) coupled to the shank <b>613</b> in this embodiment of the invention by using a submerged arc weld process to form a weld joint therebetween. The crossover component (not shown), which is manufactured from a tubular steel material, is coupled to the bit body <b>611</b> by pulsed MIG process to form a weld joint therebetween in order to allow the complex tungsten carbide material, when used, to be securely retained to the shank <b>613</b>. It is recognized that the support <b>619</b>, particularly for other materials used to faun a bit body, may be made from a unitary material piece or multiple pieces of material in a configuration differing from the shank <b>613</b> being coupled to the crossover by weld joints as presented. The shank <b>613</b> of the drill bit <b>610</b> includes conventional male threads <b>612</b> configured to API (American Petroleum Institute) standards and adapted for connection to a component of a drill string, not shown. The face <b>614</b> of the bit body <b>611</b> has mounted thereon a plurality of cutting elements <b>616</b>, each comprising a polycrystalline diamond (PCD) table <b>618</b> formed on a cemented tungsten carbide substrate. The cutting elements <b>616</b>, conventionally secured in respective cutter pockets <b>621</b> by brazing, for example, are positioned to cut a subterranean formation being drilled when the drill bit <b>610</b> is rotated under weight-on-bit (WOB) in a borehole. The bit body <b>611</b> may include gage trimmers <b>623</b> including the aforementioned PCD tables <b>618</b> configured with a flat edge aligned parallel to the rotational axis (not shown) of the drill bit <b>610</b> to trim and hold the gage diameter of the borehole, and gage pads <b>622</b> on the gage which contact the walls of the borehole to maintain the hole diameter and stabilize the drill bit <b>610</b> in the hole.

During drilling, drilling fluid is discharged through nozzle assemblies <b>630</b> located in sleeve ports <b>628</b> in fluid communication with the face <b>614</b> of bit body <b>611</b> for cooling the PCD tables <b>618</b> of cutting elements <b>616</b> and removing formation cuttings from the face <b>614</b> of drill bit <b>610</b> into passages <b>615</b> and junk slots <b>617</b>.

In <figref idref="DRAWINGS">FIG. 2</figref>, as shown by the dashed lines, an interior of roller cone <b>10</b> of drill bit <b>1</b> of <figref idref="DRAWINGS">FIG. 1</figref> includes a cylindrical journal race <b>40</b> and a semi-torus shaped ball race <b>42</b>. Journal race <b>40</b> and ball race <b>42</b> are internal bearing surfaces that are machined finish after hardfacing <b>38</b> (see <figref idref="DRAWINGS">FIG. 4</figref>) has been applied to teeth <b>20</b>. <figref idref="DRAWINGS">FIG. 2A</figref> is a cross-sectional view illustrating one of the rotatable cutter assemblies <b>514</b> of the earth-boring drill bit <b>510</b> shown in <figref idref="DRAWINGS">FIG. 1A</figref>. As shown, each bit leg <b>516</b> may include a bearing pin <b>528</b>. The cone <b>522</b> may be supported by the bearing pin <b>528</b>, and the cone <b>522</b> may be rotatable about the bearing pin <b>528</b>. Each cone <b>522</b> may have a central cone cavity <b>530</b> that may be cylindrical and may form a journal bearing surface adjacent the bearing pin <b>528</b>. The cone cavity <b>530</b> may have a flat thrust shoulder <b>532</b> for absorbing thrust imposed by the drill string (not shown) on the cone <b>522</b>. As illustrated in this example, the cone <b>522</b> may be retained on the bearing pin <b>528</b> by a plurality of locking balls <b>534</b> located in mating grooves formed in the surfaces of the cone cavity <b>530</b> and the bearing pin <b>528</b>. Additionally, a seal assembly <b>536</b> may seal bearing spaces between the cone cavity <b>530</b> and the bearing pin <b>528</b>. The seal assembly <b>536</b> may be a metal face seal assembly, as shown, or may be a different type of seal assembly, such as an elastomer seal assembly. Lubricant may be supplied to the bearing spaces between the cone cavity <b>530</b> and the bearing pin <b>528</b> by lubricant passages <b>538</b>. The lubricant passages <b>538</b> may lead to a reservoir that includes a pressure compensator <b>540</b> (<figref idref="DRAWINGS">FIG. 1A</figref>).

As previously mentioned, the cone <b>522</b> may comprise a sintered particle-matrix composite material that comprises a plurality of hard particles dispersed through a matrix material. In some embodiments, the cone <b>522</b> may be predominantly comprised of the particle-matrix composite material.

<figref idref="DRAWINGS">FIG. 2B</figref> is a cross section of a cone <b>522</b> formed after assembling the various green components to form a structure sintered to a desired final density to form the fully sintered structure shown in <figref idref="DRAWINGS">FIG. 2B</figref>. During the sintering process of the cone <b>522</b>, including the apertures <b>562</b> or other features, the cutting inserts <b>524</b> or other cutting elements, and bearing structures <b>568</b> may undergo shrinkage and densification. Furthermore, the cutting inserts <b>524</b> and the bearing structures <b>568</b> may become fused and secured to the cone <b>522</b> to provide a substantially unitary cutter assembly <b>514</b> (see <figref idref="DRAWINGS">FIG. 2A</figref>).

After the cutter assembly <b>514</b>′ has been sintered to a desired final density, various features of the cutter assembly <b>514</b>′ may be machined and polished, as necessary or desired. For example, bearing surfaces on the bearing structures <b>568</b> may be polished. Polishing the bearing surfaces of the bearing structures <b>568</b> may provide a relatively smoother surface finish and may reduce friction at the interface between the bearing structures <b>568</b> and the bearing pin <b>528</b> (<figref idref="DRAWINGS">FIG. 2A</figref>). Furthermore, the sealing edge <b>572</b> of the bearing structures <b>568</b> also may be machined and/or polished to provide a shape and surface finish suitable for sealing against a metal or elastomer seal, or for sealing against a sealing surface located on the bit body <b>512</b> (<figref idref="DRAWINGS">FIG. 1A</figref>).

The cutting inserts <b>524</b>, lands <b>523</b>, and bearing structures <b>568</b> may be formed from particle-matrix composite materials. The material composition of each of the cutting inserts <b>524</b>, lands <b>523</b>, bearing structures <b>568</b>, and cone <b>522</b> may be separately and individually selected to exhibit physical and/or chemical properties tailored to the operating conditions to be experienced by each of the respective components. By way of example, the composition of the cutting inserts <b>524</b> and the lands <b>523</b> may be selected so as to form cutting inserts <b>524</b> comprising a particle-matrix composite material that exhibits a different hardness, wear resistance, and/or toughness different from that exhibited by the particle-matrix composite material of the cone <b>522</b>.

The cutting inserts <b>524</b> and lands <b>523</b> may be formed from a variety of particle-matrix composite material compositions. The particular composition of any particular cutting insert <b>524</b> and lands <b>523</b> may be selected to exhibit one or more physical and/or chemical properties tailored for a particular earth formation to be drilled using the drill bit <b>510</b> (<figref idref="DRAWINGS">FIG. 1A</figref>). Additionally, cutting inserts <b>524</b> and lands <b>523</b> having different material compositions may be used on a single cone <b>522</b>.

By way of example, in some embodiments of the present invention, the cutting inserts <b>524</b> and the lands <b>523</b> may comprise a particle-matrix composite material that includes a plurality of hard particles that are harder than a plurality of hard particles of the particle-matrix composite material of the cone <b>522</b>. The concentration of the hard particles in the particle-matrix composite material of the cutting inserts <b>524</b> and the lands <b>523</b> may be greater than a concentration of hard particles in a particle-matrix composite material of the cone <b>522</b>.

<figref idref="DRAWINGS">FIG. 3</figref> is an isometric view of a steel-tooth <b>20</b> located on steel-tooth roller cone <b>10</b> of <figref idref="DRAWINGS">FIG. 2</figref>. Tooth <b>20</b> has an included tooth angle of θ degrees formed at a vertex <b>36</b>. Tooth <b>20</b> has a leading flank <b>22</b> and an opposite trailing flank <b>24</b>. Leading flank <b>22</b> and trailing flank <b>24</b> are joined at crest <b>26</b>, which is the top of tooth <b>20</b>. A generally triangular outer end <b>28</b> is formed between leading flank <b>22</b>, trailing flank <b>24</b>, and crest <b>26</b>. On the opposite side of tooth <b>20</b>, a generally triangular inner end <b>30</b> is formed between leading flank <b>22</b>, trailing flank <b>24</b>, and crest <b>26</b>. A base <b>32</b> broadly defines the bottom of tooth <b>20</b> and the intersection of tooth <b>20</b> with roller cone <b>10</b>. Various alternatively shaped teeth on roller cone <b>10</b> may be used, such as teeth having T-shaped crests. Tooth <b>20</b> represents a common shape for a tooth, but the system and method of the present invention may be used on any shape of tooth.

To prevent early wear and failure of drill bit <b>1</b> (see <figref idref="DRAWINGS">FIG. 1</figref>), it is necessary to apply an extremely wear-resistant material, or hardfacing <b>38</b>, to surfaces <b>22</b>, <b>24</b>, <b>26</b>, <b>28</b>, and <b>30</b> of tooth <b>20</b>. <figref idref="DRAWINGS">FIG. 4</figref> is an isometric view of a typical steel-tooth <b>20</b> such having hardfacing <b>38</b> applied to surfaces <b>22</b>, <b>24</b>, <b>26</b>, <b>28</b>, and <b>30</b>, as shown in <figref idref="DRAWINGS">FIG. 3</figref>.

<figref idref="DRAWINGS">FIGS. 5 and 5A</figref> are schematic illustrations of the system of the present invention. Seen in <figref idref="DRAWINGS">FIG. 5</figref> is an industrial robot <b>100</b> having a stationary base <b>102</b> and an articulated aim <b>104</b>. Articulated arm <b>104</b> has a distal end <b>106</b>. Robot <b>100</b> has a plurality of axes of rotation <b>108</b> about which controllable movement permits wide-range positioning of distal end <b>106</b> relative to base <b>102</b>. Robot <b>100</b> has six or more independently controllable axes of movement between base <b>102</b> and the distal end <b>106</b> of arm <b>104</b>. <figref idref="DRAWINGS">FIG. 5A</figref> illustrates a drill bit <b>610</b> attached to the articulated arm <b>104</b>, although drill bit <b>610</b> or drill bit <b>1</b> (see <figref idref="DRAWINGS">FIG. 1</figref>) or portions of any drill bit may be attached to articulated arm <b>104</b> for the application of hardfacing to portions thereof.

Robot <b>100</b> has a handling capacity of at least 125 kg, and articulated arm <b>104</b> has a wrist torque rating of at least 750 nm. Examples of industrial robots that are commercially available include models IRB 6600/IRB 6500, which are available from ABB Robotics, Inc., 125 Brown Road, Auburn Hills, Mich., USA, 48326-1507.

An adapter <b>110</b> is attached to distal end <b>106</b>. Adapter <b>110</b> has a ground connector <b>112</b> (see <figref idref="DRAWINGS">FIG. 7</figref>) for attachment to an electrical ground cable <b>114</b>. A chuck <b>120</b> is attached to adapter <b>110</b>. Chuck <b>120</b> securely grips roller cone <b>10</b> at journal bearing surface <b>40</b> (see <figref idref="DRAWINGS">FIG. 2</figref>) and/or ball race <b>42</b> (see <figref idref="DRAWINGS">FIG. 2</figref>), as shown in greater detail in <figref idref="DRAWINGS">FIGS. 8 and 9</figref>.

A heat sink, or thermal barrier, is provided between roller cone <b>10</b> and adapter <b>110</b> to prevent heat from causing premature failure of the rotating axis at distal end <b>106</b> of articulated arm <b>104</b>. The thermal barrier is an insulating spacer (not shown) located between roller cone <b>10</b> and distal end <b>106</b> of robot <b>100</b>. Alternatively, roller cone <b>10</b> may be gripped in a manner that provides an air space between roller cone <b>10</b> and distal end <b>106</b> of robot <b>100</b> to dissipate heat.

A robot controller <b>130</b> is electrically connected to robot <b>100</b> for programmed manipulation of robot <b>100</b>, including movement of articulated arm <b>104</b>. An operator pendant <b>137</b> may be provided as electrically connected to robot controller <b>130</b> for convenient operator interface with robot <b>100</b>. A sensor controller <b>140</b> is electrically connected to robot controller <b>130</b>. Sensor controller <b>140</b> may also be electrically connected to a programmable logic controller <b>150</b>.

A plurality of sensors <b>142</b> are electrically connected to sensor controller <b>140</b>. Sensors <b>142</b> include a camera <b>144</b> and/or a contact probe <b>146</b>. Alternatively, sensors <b>142</b> include a suitable laser proximity indicator <b>148</b> (illustrated as an arrow). Other types of sensors <b>142</b> may also be used. Sensors <b>142</b> provide interactive information to robot controller <b>130</b>, such as the distance between a tooth <b>20</b> on roller cone <b>10</b> and torch <b>300</b>.

A programmable logic controller <b>150</b> is electrically connected to robot controller <b>130</b>. Programmable logic controller (PLC) <b>150</b> provides instructions to auxiliary controllable devices that operate in coordinated and programmed sequence with robot <b>100</b>.

A powder dosage system <b>160</b> is provided for dispensing hardfacing powder to the system. A driver <b>162</b> is electrically connected to PLC <b>150</b> for dispensing the powder at a predetermined, desired rate.

A pilot arc power source <b>170</b> and a main arc power source <b>172</b> are electrically connected to PLC <b>150</b>. A cooling unit <b>174</b> is electrically connected to PLC <b>150</b>. In a preferred embodiment, a data-recording device <b>195</b> is electrically connected to PLC <b>150</b>.

A gas dispensing system <b>180</b> is provided. A transport gas source <b>182</b> supplies transport gas through a flow controller <b>184</b> to carry or transport hardfacing welding powder to torch <b>300</b>. Flow controller <b>184</b> is electrically connected to PLC <b>150</b>, which controls the operation of flow controller <b>184</b> and the flow and flow rate of the transport gas. A plasma gas source <b>186</b> supplies gas for plasma formation through a flow controller <b>188</b>. Flow controller <b>188</b> is electrically connected to PLC <b>150</b>, which controls the operation of flow controller <b>188</b> and the flow and flow rate of the plasma gas. Similarly, a shielding gas source <b>190</b> supplies shielding gas through a flow controller <b>192</b>. Flow controller <b>192</b> is electrically connected to PLC <b>150</b>, which controls the operation of flow controller <b>192</b> and the flow and flow rate of the shielding gas. It is known to utilize a single gas source for more than one purpose, e.g., plasma, shielding, and transport. Thus, different, multiple flow controllers connected in a series alignment can control the flow and flow rate of gas from a single gas source.

The torch <b>300</b> comprises a plasma transferred arc (PTA) torch, that receives hardfacing welding powder from powder dosage system <b>160</b>, and plasma, transport, and shielding gases from their respective supplies and controllers in gas dispensing system <b>180</b>. Torch <b>300</b> is secured to a positioner or positioning table <b>200</b>, which grips and manipulates torch <b>300</b>. In a preferred embodiment, positioner <b>200</b> is capable of programmed positioning of torch <b>300</b> in a substantially vertical plane. A positioner <b>200</b> has a vertical drive <b>202</b> and a horizontal drive <b>204</b>. Drives <b>202</b> and <b>204</b> may be toothed belts, ball screws, a toothed rack, pneumatic, or other means. If desired, an industrial robot <b>100</b> having six independently controllable axes of movement between base <b>102</b> and distal end <b>106</b> of arm <b>104</b> as described herein may be used as the positioner <b>200</b> having the torch <b>300</b> mounted thereon.

<figref idref="DRAWINGS">FIGS. 6 and 7</figref> are isometric views of robot <b>100</b> shown manipulating roller cone <b>10</b> secured to adapter <b>110</b> on distal end <b>106</b> of articulated arm <b>104</b> of robot <b>100</b>. As illustrated in <figref idref="DRAWINGS">FIG. 6</figref> and in <figref idref="DRAWINGS">FIGS. 13-16</figref>, the several axes of rotation <b>108</b> provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of any tooth <b>20</b> of roller cone <b>10</b> directly beneath torch <b>300</b>. As illustrated in <figref idref="DRAWINGS">FIG. 7</figref>, roller cone <b>10</b> is positioned beneath torch <b>300</b> in preparation for the application of hardfacing <b>38</b> (see <figref idref="DRAWINGS">FIG. 4</figref>).

Adapter <b>110</b> is aligned by indicator with articulated arm <b>104</b>. Adapter <b>110</b> is aligned to run substantially true with a programmable axis of movement of robot <b>100</b>. A chuck <b>120</b> is attached to adapter <b>110</b> and indicator aligned to within 0.005 inch of true center rotation. Roller cone <b>10</b> is held by chuck <b>120</b> and also centered by indicator alignment. Roller cone <b>10</b> has grooves that permit location and calibration of the end of torch <b>300</b>. Electrode <b>304</b> (see <figref idref="DRAWINGS">FIG. 11</figref>) of torch <b>300</b> is then used to align roller cone <b>10</b> about the z-axis of rotation of roller cone <b>10</b> by robot <b>100</b>.

As illustrated in <figref idref="DRAWINGS">FIG. 7</figref>, electrical ground cable <b>114</b> is electrically connected to adapter <b>110</b> by ground connector <b>112</b>, a rotatable sleeve connector. Alternatively, ground connector <b>112</b> is a brush connector. Ground cable <b>114</b> is supported by a tool balancer (not shown) to keep it away from the heat of roller cone <b>10</b> and the welding arc during hardfacing operations. Chuck <b>120</b> is attached to adapter <b>110</b>. Roller cone <b>10</b> is held by chuck <b>120</b>.

As roller cones <b>10</b> are manipulated vertically, horizontally, inverted, and rotated beneath torch <b>300</b>, highly secure attachment of roller cone <b>10</b> to robot <b>100</b> is required for safety and accuracy of the hardfacing operation. Precision alignment of roller cones <b>10</b> in relation to chuck <b>120</b> is also necessary to produce a quality hardfacing and to avoid material waste.

<figref idref="DRAWINGS">FIG. 8</figref> is an isometric view of chuck <b>120</b>, a three jaw chuck, having adjustable jaws <b>122</b> for gripping a hollow interior of a roller cone <b>10</b>. Jaws <b>122</b> are specially profiled to include a cylindrical segment shaped journal land <b>124</b>, which contacts journal race <b>40</b> on roller cone <b>10</b>, providing highly secure attachment of roller cone <b>10</b> on chuck <b>120</b> of robot <b>100</b>. A seal relief <b>128</b> is provided to accommodate a seal supporting surface on roller cone <b>10</b>.

Illustrated in <figref idref="DRAWINGS">FIG. 9</figref>, a jaw <b>122</b> of chuck <b>120</b> is specially profiled to include a semi-torus shaped race land <b>126</b> above journal land <b>124</b>. In this configuration, journal land <b>124</b> fits in alignment with journal race <b>40</b> (see <figref idref="DRAWINGS">FIG. 2</figref>) and race land <b>126</b> fits in alignment with ball race <b>42</b> (<figref idref="DRAWINGS">FIG. 2</figref>), providing precise alignment against the centerline of ball race <b>42</b> and secure attachment of roller cone <b>10</b> on chuck <b>120</b> of robot <b>100</b>. Seal relief <b>128</b> may be provided to accommodate a seal supporting surface on roller cone <b>10</b>.

<figref idref="DRAWINGS">FIG. 10</figref> is a schematic side view of positioner <b>200</b> and torch <b>300</b>. As illustrated, positioner <b>200</b> has a clamp <b>206</b> for holding torch <b>300</b> in a secure and substantially vertical orientation. Vertical drive <b>202</b> provides controlled movement of torch <b>300</b> along the z-axis. Drive <b>203</b> connected to PLC <b>150</b> (<figref idref="DRAWINGS">FIG. 5</figref>) rotates the torch <b>300</b> of positioner <b>200</b> about the z-axis of the support <b>201</b>. Drive <b>205</b> connected to the PLC <b>150</b> rotates torch <b>300</b> of positioner <b>200</b> about the z-axis of support <b>207</b>. Drive <b>209</b> connected to the PLC <b>150</b> rotates torch <b>300</b> of positioner <b>200</b> about the y-axis of clamp <b>206</b>. Horizontal drive <b>204</b> provides controlled movement of torch <b>300</b> along the y-axis. In combination, drives <b>202</b> and <b>204</b> provide controlled movement of torch <b>300</b> on a vertical plane. Drives <b>202</b> and <b>204</b> are electrically connected to PLC <b>150</b>.

Drive <b>204</b> oscillates torch <b>300</b> along the horizontal y-axis in response to PLC <b>150</b> for programmed application of a wide-path bead of hardfacing <b>38</b> on the surface of teeth <b>20</b> of roller cone <b>10</b> (see <figref idref="DRAWINGS">FIG. 2</figref>). Drive <b>202</b> moves torch <b>300</b> along the vertical z-axis in real-time response to measured changes in the voltage or current between torch <b>300</b> and roller cone <b>10</b>. These occasional real-time distance adjustments maintain the proper energy level of the transferred arc between torch <b>300</b> and roller cone <b>10</b>.

Gas dispensing system <b>180</b> is connected by piping or tubing to torch <b>300</b> for the delivery of transport gas, plasma gas and shielding gas. Hardfacing powder is delivered to torch <b>300</b> within the stream of flowing transport gas which receives the hardfacing powder from powder dosage system <b>160</b> (see <figref idref="DRAWINGS">FIGS. 5 and 5A</figref>). Torch <b>300</b> is electrically connected to pilot arc power source <b>170</b> and main arc power source <b>172</b>.

<figref idref="DRAWINGS">FIG. 11</figref> is a schematic cross-section of torch <b>300</b>. Torch <b>300</b> has a nozzle <b>302</b> that comprises a Plasma Transferred Arc (PTA) torch. A non-burning tungsten electrode (cathode) <b>304</b> is centered in nozzle <b>302</b> and a nozzle annulus <b>306</b> is formed between nozzle <b>302</b> and electrode <b>304</b>. Nozzle annulus <b>306</b> is connected to plasma gas source <b>186</b> (<figref idref="DRAWINGS">FIG. 5</figref>) to allow the flow of plasma between nozzle <b>302</b> and electrode <b>304</b>. A restricted orifice <b>314</b> accelerates the flow of plasma gas exiting nozzle <b>302</b>. In this embodiment, nozzle annulus <b>306</b> is connected to powder dosage system <b>160</b> (not shown), which supplies hardfacing powder carried by transport gas to nozzle annulus <b>306</b>.

Electrode <b>304</b> is electrically insulated from nozzle <b>302</b>. A pilot arc circuit <b>330</b> is electrically connected to pilot arc power source <b>170</b> (<figref idref="DRAWINGS">FIG. 5</figref>), and electrically connects nozzle <b>302</b> to electrode <b>304</b>. A main arc circuit <b>332</b> is electrically connected to main arc power source <b>172</b> (<figref idref="DRAWINGS">FIG. 5</figref>), and electrically connects electrode <b>304</b> to the anode work piece, roller cone <b>10</b>. An insulator separates pilot arc circuit <b>330</b> and main arc circuit <b>332</b>. A cooling channel <b>316</b> is provided in nozzle <b>302</b> for connection to a pair of conduits <b>176</b>, <b>178</b> that circulate cooling fluid from cooling unit <b>174</b> (<figref idref="DRAWINGS">FIGS. 5 and 5A</figref>).

A gas cup <b>320</b> surrounds nozzle <b>302</b>. Nozzle <b>302</b> is electrically insulated from gas cup <b>320</b>. A cup annulus <b>322</b> is formed between gas cup <b>320</b> and nozzle <b>302</b>. Cup annulus <b>322</b> is connected to shielding gas source <b>190</b> (see <figref idref="DRAWINGS">FIG. 5</figref>) to allow the flow of shielding gas between gas cup <b>320</b> and nozzle <b>302</b>.

A small, non-transferred pilot arc burns between non-melting (non-consumable) tungsten electrode <b>304</b> (cathode) and nozzle <b>302</b> (anode). A transferred arc burns between electrode <b>304</b> (cathode) and roller cone <b>10</b> (anode). Electrode <b>304</b> is the negative pole and roller cone <b>10</b> is the positive pole. Pilot arc circuit <b>330</b> is ignited to reduce the resistance to an arc jumping between roller cone <b>10</b> and electrode <b>304</b> when voltage is applied to main arc circuit <b>332</b>. A ceramic insulator separates circuits <b>330</b> and <b>332</b>.

Plasma Transferred Arc (PTA) welding is similar to Tungsten Inert Gas (TIG) welding. Torch <b>300</b> is supplied with plasma gas, shielding gas, and transport gas, as well as hardfacing powder. Plasma gas from plasma gas source <b>186</b> (see <figref idref="DRAWINGS">FIG. 5</figref>) is delivered through nozzle <b>302</b> to electrode <b>304</b>. The plasma gas exits nozzle <b>302</b> through orifice <b>314</b>. When amperage from main arc circuit <b>332</b> is applied to electrode <b>304</b>, the jet created from exiting plasma gas turns into plasma. Plasma gas source <b>186</b> is comprised of 99.9% argon.

Shielding gas from shielding gas source <b>190</b> (see <figref idref="DRAWINGS">FIG. 5</figref>) is delivered to cup annulus <b>322</b>. As the shielding gas exits cup annulus <b>322</b> it is directed toward the work piece, roller cone <b>10</b>. The shielding gas forms a cylindrical curtain surrounding the plasma column, and shields the generated weld puddle from oxygen and other chemically active gases in the air. Shielding gas source <b>190</b> is 95% argon and 5% hydrogen.

Transport gas source <b>182</b> is connected to powder dosage system <b>160</b>, as shown in <figref idref="DRAWINGS">FIGS. 5 and 5A</figref>. Powder dosage system <b>160</b> meters hardfacing powder through a conduit connected to nozzle <b>302</b> at the proper rate for deposit. The transport gas from transport gas source <b>182</b> carries the metered powder to nozzle <b>302</b> and to the weld deposit on roller cone <b>10</b>.

<figref idref="DRAWINGS">FIG. 12</figref> is a cross-section of torch <b>300</b> wherein gas cup <b>320</b> of torch <b>300</b> has a diameter of less than 0.640 inch and a length of less than 4.40 inches. Nozzle <b>302</b> (anode) of torch <b>300</b> is made of copper and is liquid cooled. One such torch that is commercially available is the Eutectic E52 torch available from Castolin Eutectic Group, Gutenbergstrasse 10, 65830 Kriftel, Germany.

Gas cup <b>320</b> is modified from commercially available gas cups for use with torch <b>300</b> in that gas cup <b>320</b> extends beyond nozzle <b>302</b> by no more than approximately 0.020 inch. As such, gas cup <b>320</b> has an overall length of approximately 4.375 inches. As seen in the embodiment, transport gas and powder are delivered through a transport gas port <b>324</b> in nozzle <b>302</b>. An insulating material is attached to the exterior of gas cup <b>320</b> of the torch <b>300</b> for helping to prevent short-circuiting and damage to torch <b>300</b>.

The shielding of gas cup <b>320</b> described above is specially designed to improve shield gas coverage of the melt puddle for reducing the porosity thereof. This permits changing the orientation of gas cup <b>320</b> to nozzle (anode) <b>302</b> and reduction of shielding gas flow velocity. This combination significantly reduces porosity that results from attempts to use presently available commercial equipment to robotically apply hardfacing <b>38</b> to steel-tooth roller cones <b>10</b>.

OPERATION

Some of the problems encountered in the development of robotic hardfacing included interference between the torch and teeth on the roller cone, short circuiting the torch, inconsistent powder flow, unsustainable plasma column, unstable puddle, heat buildup when using conventional welding parameters, overheated weld deposits, inconsistent weld deposits, miss-shaping of teeth, and other issues. As a result, extensive experimentation was required to reduce the present invention to practice.

As described herein, the system and method of the present invention begins with inverting what has been the conventional practice of roller cones. That is, the practice of maintaining roller cone <b>10</b> generally stationary and moving torch <b>300</b> all over it at various angles as necessary. Fundamental to the system and method of the present invention, torch <b>300</b> is preferably held substantially vertical, although it may be held at any angle or attitude desired through the use of a positioner <b>200</b> or robotic arm <b>100</b>, while roller cone <b>10</b> is held by chuck <b>120</b> of robotic arm <b>104</b> and manipulated beneath torch <b>300</b>. If torch <b>300</b> is robotically manipulated by positioner <b>200</b> or robotic aim <b>104</b> in varying and high angular positions relative to vertical, hardfacing powder in torch <b>300</b> will flow unevenly and cause torch <b>300</b> to become plugged. In addition to plugging torch <b>300</b>, even flow of hardfacing powder is critical to obtaining a consistent quality bead of hardfacing material on roller cone <b>10</b>. Thus, deviation from a substantially vertical orientation is avoided. Although, if plugging of torch <b>300</b> is not a problem with the particular hardfacing being used, the torch <b>300</b> may be oriented at any desired position.

As the terms are used in this specification and claims, the words “generally” and “substantially” are used as descriptors of approximation, and not words of magnitude. Thus, they are to be interpreted as meaning “largely but not necessarily entirely.”

Accordingly, a roller cone <b>10</b> is secured to distal end <b>106</b> of robot arm <b>104</b> by chuck <b>120</b> and adapter <b>110</b>. Roller cone <b>10</b> is grounded by ground cable <b>114</b> which is attached to adapter <b>110</b> at ground connector <b>112</b>. Providing an electrical ground source near distal end <b>106</b> of robot arm <b>104</b> of robot <b>100</b> is necessary, since using robot <b>100</b> in the role-reversed manner of the present invention (holding the anode work piece) would otherwise result in destruction of the robot <b>100</b> by arc welding the rotating components of the movable axes together.

Robot arm <b>104</b> moves in response to program control from robot controller <b>130</b> and/or PLC <b>150</b>. As stated, torch <b>300</b> is mounted to positioner <b>200</b> having two controllable axes in a substantially vertical plane. As previously mentioned, a physical indicator, such as a notch or groove, may be formed on roller cone <b>10</b> to be engaged by torch <b>300</b> to ensure proper initial orientation between torch <b>300</b>, robot arm <b>104</b>, and roller cone <b>10</b>. Additionally, at least one position indicator is electrically connected to PLC <b>150</b> for determining location and orientation of roller cone <b>10</b> to be hardfaced relative to robot <b>100</b>.

After initial orientation and positioning, transfer, plasma and shielding gases are supplied to torch <b>300</b> by their respective sources <b>182</b>, <b>186</b>, <b>190</b>, through their respective controllers <b>184</b>, <b>188</b>, <b>192</b>.

Torch <b>300</b> is ignited by provision of current from pilot arc power source <b>170</b> and main arc power source <b>172</b>. Igniting pilot arc circuit <b>330</b> reduces the resistance to an arc jumping between roller cone <b>10</b> and electrode <b>304</b> when voltage is applied to main arc circuit <b>332</b>.

Flow of hardfacing powder is provided by powder dosage system <b>160</b> dispensing controlled amounts of hardfacing powder into a conduit of flowing transport gas from transport gas source <b>182</b>, having a flow rate controlled by flow controller <b>184</b>. Then relative movement, primarily of roller cone <b>10</b> relative to torch <b>300</b>, as described above and below is obtained by movement of robot arm <b>104</b> and positioner <b>200</b>, permitting automated application of hardfacing <b>38</b> to the various selected surfaces of roller cone <b>10</b> in response to programming from robot controller <b>130</b> and PLC <b>150</b>.

An imaging sensor <b>142</b> may be provided for identifying specific roller cones <b>10</b> and/or parts of roller cones <b>10</b> to be hardfaced. A laser sensor <b>142</b> (<figref idref="DRAWINGS">FIG. 5</figref>) may also provided for determining proximity of torch <b>300</b> to roller cone <b>10</b> and tooth <b>20</b>, and/or to measure thickness of applied hardfacing <b>38</b>. Positioning and other programming parameters are correctable based on sensor <b>142</b> data acquisition and processing.

Robot controller <b>130</b> is primarily responsible for control of robot arm <b>104</b>, while PLC <b>150</b> and data recording device <b>195</b> provide sensor <b>142</b> data collection and processing, data analysis and process adjustment, adjustments in robot <b>100</b> movement, torch <b>300</b> oscillation, and torch <b>300</b> operation, including power, gas flow rates and material feed rates.

<figref idref="DRAWINGS">FIGS. 13</figref>, <b>13</b>A, and <b>14</b> illustrate robot <b>100</b> manipulating roller cone <b>10</b> into position to apply hardfacing material to outer end <b>28</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) of teeth <b>20</b> (see <figref idref="DRAWINGS">FIGS. 2-4</figref>) on outer row <b>16</b> of roller cone <b>10</b> (see <figref idref="DRAWINGS">FIG. 2</figref>). <figref idref="DRAWINGS">FIG. 15</figref> illustrates torch <b>300</b> in position to apply hardfacing to leading flank <b>22</b> or trailing flank <b>24</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) of tooth <b>20</b> (see <figref idref="DRAWINGS">FIGS. 2-4</figref>) on outer row <b>16</b> (see <figref idref="DRAWINGS">FIG. 16</figref>) of roller cone <b>10</b> (see <figref idref="DRAWINGS">FIG. 2</figref>). <figref idref="DRAWINGS">FIG. 16</figref> is an isometric view illustrating robot <b>100</b> manipulating roller cone <b>10</b> (see <figref idref="DRAWINGS">FIG. 2</figref>) into position in preparation for application of hardfacing <b>38</b> (see <figref idref="DRAWINGS">FIG. 4</figref>) to inner end <b>30</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) of tooth <b>20</b> (see <figref idref="DRAWINGS">FIGS. 2-4</figref>).

As can be seen in <figref idref="DRAWINGS">FIG. 6</figref> and in <figref idref="DRAWINGS">FIGS. 13-16</figref>, several axes of rotation <b>108</b> of robot arm <b>100</b> provide sufficient degrees of freedom to permit vertical, horizontal, inverted, and rotated positioning of roller cone <b>10</b> beneath torch <b>300</b>, allowing torch <b>300</b> to access the various surfaces of roller cone <b>10</b> while maintaining torch <b>300</b> in a substantially vertical position. In addition to providing a system and apparatus that addresses the realities of automated application of hardfacing to the complex surfaces of roller cones, the present invention provides a system and method or pattern of application of the hardfacing material to the cutters that is adapted to take advantage of the precisely controlled relative movement between torch <b>300</b> and roller cone <b>10</b> made possible by the apparatus of the present invention. These patterns will be described with reference to <figref idref="DRAWINGS">FIGS. 17 through 25</figref> below.

The above-described system and method of the present invention has resolved these issues and enabled development of the method of applying hardfacing of the present invention. The present invention includes a hardfacing pattern created by superimposing a first waveform path onto a second waveform path.

<figref idref="DRAWINGS">FIG. 17</figref> is a bottom view of a typical steel-tooth <b>20</b>, such as might be located on roller cone <b>10</b>, illustrating a first waveform target path <b>50</b> defined in accordance with the present invention. Tooth <b>20</b> has an actual or approximate included angle θ. Vertex <b>36</b> of included angle θ lies on centerline <b>34</b> of tooth <b>20</b>. Centerline <b>34</b> extends through crest <b>26</b> and base <b>32</b>.

As illustrated, target path <b>50</b> traverses one surface of tooth <b>20</b>. By way of example, outer end surface <b>28</b> is shown, but applies to any and all surfaces of tooth <b>20</b>. Target path <b>50</b> has numerous features. Target path <b>50</b> may begin with a strike path <b>52</b> located near crest <b>26</b>. The various surfaces of teeth <b>20</b> are preferably welded from nearest crest <b>26</b> toward base <b>32</b>, when possible, to control heat buildup.

Thereafter, target path <b>50</b> traverses the surface of tooth <b>20</b> in parallel paths while progressing in the direction of base <b>32</b>. Target path <b>50</b> is comprised of traversing paths <b>54</b>, which cross centerline <b>34</b>, are alternating in direction, and generally parallel to crest <b>26</b>.

Step paths <b>56</b> connect traversing paths <b>54</b> to form a continuous target path <b>50</b>. Step paths <b>56</b> are not reversing, but progressing in the direction of base <b>32</b>. Step paths <b>56</b> are preferably generally parallel to the sides of the surface being hardfaced. As such, step paths <b>56</b> are disposed at an angle of approximately θ/2 to centerline <b>34</b>. Taken together, traversing paths <b>54</b> and step paths <b>56</b> form target path <b>50</b> as a stationary, generally trapezoidal waveform about centerline <b>34</b>, having an increasing amplitude in the direction of base <b>32</b>.

The amperage of torch <b>300</b> is applied in proportion to the length of traversing path <b>54</b>. This permits generation of a good quality bead definition in hardfacing <b>38</b>. This is obtained by starting at the lowest amperage on traversing path <b>54</b> nearest to crest <b>26</b> of tooth <b>20</b>, and increasing the amperage in proportion to the length of traversing path <b>54</b> where hardfacing <b>38</b> is being applied.

Alternatively, amperage and powder flow are increased as hardfacing <b>38</b> is applied to crest <b>26</b>. This results in increased height of the automatically welded crests <b>26</b> to their total design height. The programmed traversing paths <b>54</b> for flanks <b>22</b> and <b>24</b>, inner surface <b>30</b> and outer surface <b>28</b> (see <figref idref="DRAWINGS">FIG. 3</figref>) are also modified such that to overlap crests <b>26</b> sufficiently to create the desired profile and to provide sufficient support to crests <b>26</b>.

The program sequence welds the surface of a datum tooth, then offsets around the roller cone axis the amount needed to align with the next tooth surface. Also, teeth are welded from the tip to the root to enhance heat transfer from the tooth and prevent heat buildup. Welding is alternated between rows of teeth on the roller cone to reduce heat buildup.

<figref idref="DRAWINGS">FIG. 18</figref> is a schematic representation of the oscillation of torch <b>300</b>. In this illustration, x-y defines a horizontal plane. Torch <b>300</b> is movable in the z-y vertical plane perpendicular to the x-y plane. The y-axis is the axis of oscillation (“AO”). Torch <b>300</b> is oscillated along the AO. The oscillation midpoint is identified as OM. Oscillation of torch <b>300</b> is controlled by instructions from programmable logic controller <b>150</b> provided to horizontal drive <b>204</b> of positioner <b>200</b> (see <figref idref="DRAWINGS">FIG. 5</figref>). Torch <b>300</b> has a variable linear velocity along its axis of oscillation AO depending upon the characteristics of the roller cone material and the hardfacing being applied.

<figref idref="DRAWINGS">FIG. 19</figref> is a schematic representation of a second waveform torch path <b>60</b> formed in accordance with the present invention. Hardfacing is applied to a tooth <b>20</b> by oscillating torch <b>300</b> while moving roller cone <b>10</b> on target path <b>50</b> beneath torch <b>300</b>. In this manner, hardfacing is applied by superimposing the waveform of torch path <b>60</b> onto the waveform of target path <b>50</b>. By superimposing torch path <b>60</b> onto target path <b>50</b>, a superior hardfacing pattern is created. More specifically, the superimposed waveform generates a uniform and continuous hardfacing bead, is properly defined, and efficiently covers the entire surface of tooth <b>20</b> with the desired thickness of material and without excessive heat buildup.

As used throughout herein, the terms “waveform,” “trapezoidal waveform” and “triangular waveform” are not intended to be construed or interpreted by any resource other than the drawings and description provided herein. More specifically, they are used only as descriptors of the general path shapes to which they have been applied herein.

As seen in <figref idref="DRAWINGS">FIG. 19</figref>, torch path <b>60</b> has an amplitude Λ. It is preferred to have a Λ between 3 mm and 5 mm. It is more preferred to have a Λ is about 4 mm. Traversing path <b>54</b> (see <figref idref="DRAWINGS">FIG. 17</figref>) is positioned in approximate perpendicular relationship to the axis of torch <b>300</b> oscillation, at the oscillation midpoint (OM). The waveform of torch path <b>60</b> is formed by oscillating torch <b>300</b> while moving roller cone <b>10</b> along traversing path <b>54</b> (see <figref idref="DRAWINGS">FIG. 17</figref>) beneath the OM of torch <b>300</b>. Thus, traversing path <b>54</b> of target path <b>50</b> (see <figref idref="DRAWINGS">FIG. 17</figref>) becomes the axis about which the generally triangular waveform of torch path <b>60</b> oscillates.

The torch path <b>60</b> has a velocity of propagation V_tof between 1.2 mm and 2.5 mm per second at the intersection of traversing path <b>54</b> and OM of torch <b>300</b>. Roller cone <b>10</b> is positioned and moved by instructions from robot controller <b>130</b> provided to robot <b>100</b>. Robot <b>100</b> moves roller cone <b>10</b> to align target path <b>50</b> directly beneath the OM. Roller cone <b>10</b> is moved such that the OM progresses along target path <b>50</b> at a linear velocity (target path speed) of between 1 mm and 2.5 mm per second.

As illustrated, a momentary dwell period <b>68</b> is programmed to elapse between peaks of oscillation of torch <b>300</b>, wherein dwell period <b>68</b> helps prevent generally triangular waveform of torch path <b>60</b> from being a true triangular waveform. Preferably, dwell period <b>68</b> is between about 0.1 to 0.4 seconds.

<figref idref="DRAWINGS">FIG. 20</figref> is a schematic representation of the secondary oscillation <b>80</b> of traversing path <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) modifying torch path <b>60</b> (see <figref idref="DRAWINGS">FIG. 19</figref>). Traversing path <b>54</b> is oscillated as a function of the location of oscillation midpoint OM on target path <b>50</b> (see <figref idref="DRAWINGS">FIG. 17</figref>). Secondary oscillation <b>80</b> is created by gradually articulating roller cone <b>10</b> between step paths <b>56</b> as oscillation midpoint OM of oscillating torch <b>300</b> passes over traversing path <b>54</b>. Each traversing path <b>54</b> constitutes ½λ of a wave length of secondary oscillation <b>80</b>. Since traversing paths <b>54</b> are of different lengths, the wavelength of secondary oscillation <b>80</b> expands as the hardfacing application progresses towards base <b>32</b> of tooth <b>20</b>. For example, where α₁represents a first traversing path <b>54</b> and α₂represents the next traversing path <b>54</b>, α₁&lt;α₂.

<figref idref="DRAWINGS">FIG. 21</figref> is a bottom view of steel-tooth <b>20</b> illustrating traversing paths <b>54</b> connected by step paths <b>56</b> to form first waveform target path <b>50</b>. Second waveform torch path <b>60</b> is superimposed on target path <b>50</b>. When secondary oscillation <b>80</b> is imparted on traversing path <b>54</b>, an accordion-like alteration of second waveform torch path <b>60</b> results.

Referring to <figref idref="DRAWINGS">FIG. 20</figref> and <figref idref="DRAWINGS">FIG. 21</figref>, a maximum articulation angle of about |θ/2| of roller cone <b>10</b> occurs at each step path <b>56</b>. In an optional embodiment, as oscillation midpoint OM of torch <b>300</b> progresses on each step path <b>56</b>, secondary oscillation <b>80</b> is dwelled. This can be done optionally based on prior path (hardfacing) coverage of step path <b>56</b>. Point <b>90</b> in <figref idref="DRAWINGS">FIG. 20</figref> schematically represents the dwell periods.

As roller cone <b>10</b> moves along traversing path <b>54</b>, roller cone <b>10</b> is gradually articulated by robot <b>100</b> until axis of oscillation AO (see <figref idref="DRAWINGS">FIG. 18</figref>) is substantially perpendicular to traversing path <b>54</b> at tooth <b>20</b> centerline <b>34</b>. This occurs schematically at point <b>88</b> on <figref idref="DRAWINGS">FIG. 20</figref>. As roller cone <b>10</b> continues to move along traversing path <b>54</b>, roller cone <b>10</b> is gradually articulated by robot <b>100</b> until step path <b>56</b> is again parallel to axis of oscillation AO. This occurs when oscillation midpoint OM arrives at a subsequent step path <b>56</b>. At that point, maximum articulation of θ/2 has been imparted to roller cone <b>10</b>. Oscillation is dwelled at point <b>90</b> until oscillation midpoint OM arrives at subsequent traversing path <b>54</b>. Roller cone <b>10</b> is then gradually articulated back by robot <b>100</b> until traversing path <b>54</b> is again perpendicular to axis of oscillation AO at tooth centerline <b>34</b>. This occurs at point <b>92</b> in <figref idref="DRAWINGS">FIG. 20</figref>.

Secondary oscillation of roller cone <b>10</b> continues until subsequent step path <b>56</b> is parallel to axis of oscillation AO, when oscillation midpoint OM arrives at subsequent step path <b>56</b>. At that point, a maximum articulation of −θ/2 has been imparted to roller cone <b>10</b>. Oscillation is again dwelled at point <b>90</b> until oscillation midpoint OM arrives at subsequent traversing path <b>54</b>.

Robot <b>100</b> rotates roller cone <b>10</b> a maximum of angle θ/2 at the intersection of traversing path <b>54</b> and step path <b>56</b>, such that step path <b>56</b> and the approaching edge of tooth <b>20</b> are oriented generally parallel to axis of oscillation AO of torch <b>300</b>. The waveform of torch path <b>60</b> is thus substantially modified as torch <b>300</b> approaches each step path <b>56</b>. The application result is a very efficient and tough “shingle” pattern <b>39</b> of hardfacing <b>38</b> near tooth <b>20</b> centerline <b>34</b>. <figref idref="DRAWINGS">FIG. 24</figref> is a schematic representation of “shingle” pattern <b>39</b>.

Optionally, oscillation of roller cone <b>10</b> may be dwelled when oscillation midpoint OM is near centerline <b>34</b> of tooth <b>20</b> to obtain a more uniform bead deposition across the width of tooth <b>20</b>. In the preferred embodiment, step paths <b>56</b> are slightly offset from the edge of tooth <b>20</b> by a distance d.

The path speed of step path <b>56</b> may be higher than the path speed of traversing path <b>54</b>, such that the amount of hardfacing deposited is controlled to provide the desired edge protection for tooth <b>20</b>. It is preferred to have the length of step path <b>56</b> is greater than height Λ, and less than 2Λ. Preferably, step path <b>56</b> is approximately 5 mm. Thus, hardfacing deposited on two adjacent traversing paths <b>54</b> will overlap. Preferably, the length of overlap is about 3 mm. Generating this overlap creates a smooth surface with no crack-like defects.

Roller cone <b>10</b> may be preheated to prevent heat induced stress. When necessary, portions of the welds can be interrupted during processing to minimize and control heat buildup. Preferably, crests <b>26</b> are formed in three interrupted passes, in which the interruption provides cooling and shape stabilization of the applied material from the previous pass.

<figref idref="DRAWINGS">FIG. 22</figref> is a schematic representation of another embodiment of the system and method of the present invention wherein secondary oscillation <b>80</b> of traversing path <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) again modifies torch path <b>60</b> (see <figref idref="DRAWINGS">FIG. 19</figref>). However, in this embodiment, secondary oscillation <b>80</b> is created by relatively sudden and complete articulation of roller cone <b>10</b> at step paths <b>56</b> as oscillation midpoint OM of oscillating torch <b>300</b> reaches, or nearly reaches, step path <b>56</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>). Each traversing path <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) constitutes ½λ of a wavelength of secondary oscillation <b>80</b>. Since traversing paths <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) are of different lengths, the wavelength of secondary oscillation <b>80</b> expands as the hardfacing application progresses towards base <b>32</b> of tooth <b>20</b>. For example, where α₁represents a first traversing path <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) and α₂represents the next traversing path <b>54</b>, α₁&lt;α₂.

<figref idref="DRAWINGS">FIG. 23</figref> is a bottom view of steel-tooth <b>20</b> illustrating traversing paths <b>54</b> connected by step paths <b>56</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>) to form first waveform target path <b>50</b> (see <figref idref="DRAWINGS">FIG. 17</figref>). Second waveform torch path <b>60</b> (see <figref idref="DRAWINGS">FIG. 19</figref>) is superimposed on target path <b>50</b> (see <figref idref="DRAWINGS">FIG. 17</figref>). When secondary oscillation <b>80</b> is imparted on traversing paths <b>54</b> (see <figref idref="DRAWINGS">FIGS. 17</figref>, <b>21</b>, and <b>23</b>), a herringbone pattern of hardfacing <b>38</b> is produced on the surface of tooth <b>20</b>.

Referring to <figref idref="DRAWINGS">FIG. 22</figref> and <figref idref="DRAWINGS">FIG. 23</figref>, a maximum articulation angle of about |θ/2| of roller cone <b>10</b> occurs at each step path <b>56</b> (as measured from the centerline <b>34</b> of tooth <b>20</b>). In this embodiment, as oscillation midpoint OM of torch <b>300</b> progresses on each step path <b>56</b>, secondary oscillation <b>80</b> is dwelled. The dwell periods are schematically represented by the high and low points of secondary oscillation <b>80</b> in <figref idref="DRAWINGS">FIG. 22</figref>.

As roller cone <b>10</b> moves along traversing path <b>54</b>, it is not again articulated by robot <b>100</b> until oscillation midpoint OM of torch <b>300</b> nears or reaches the subsequent step path <b>56</b>. This occurs schematically at point <b>96</b> on <figref idref="DRAWINGS">FIG. 22</figref>. At this point, roller cone <b>10</b> is articulated by robot <b>100</b> an angular amount θ, aligning subsequent step path <b>56</b> substantially parallel to axis of oscillation AO.

A traversing row <b>54</b>A will comprise the centerline of a series of parallel columns of hardfacing <b>38</b> inclined at an angle to centerline <b>34</b> of tooth <b>20</b>. As illustrated, the angle is approximately θ/2. Additionally, traversing row <b>54</b>A will have an adjacent traversing row <b>54</b>B comprising the centerline of a series of parallel columns of hardfacing <b>38</b>, inclined at an angle to centerline <b>34</b> of tooth <b>20</b>, where the angle is approximately −(θ/2). Still, the hardfacing <b>38</b> of traversing row <b>54</b>A and the hardfacing of traversing row <b>54</b>B will overlap. The application result is a very efficient and tough “herringbone” pattern <b>41</b> of hardfacing <b>38</b> near tooth <b>20</b> centerline <b>34</b>. <figref idref="DRAWINGS">FIG. 25</figref> is a schematic representation of “herringbone” pattern <b>41</b>.

As an alternative, a scooped tooth <b>20</b> configuration is obtained by welding crest <b>26</b> in two passes. The first pass adds height. When the second pass is made without pausing, hardfacing <b>38</b> applied to crest <b>26</b> adds width and laps over to the desired side.

<figref idref="DRAWINGS">FIGS. 26A and 26B</figref> illustrate hardfacing <b>38</b> applied using the systems and methods described herein to the cutter assemblies <b>514</b> and cones <b>522</b> illustrated in <figref idref="DRAWINGS">FIG. 2A</figref> to provide protection to portions of cones of sintered materials using inserts <b>524</b> as teeth or cutters.

<figref idref="DRAWINGS">FIG. 27</figref> illustrates hardfacing <b>38</b> applied using the systems and methods described herein to a drill bit <b>610</b>, although hardfacing may be applied to any type drill bit or portions thereof as described herein.

It will be readily apparent to those skilled in the art that the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention.

Having thus described the present invention by reference to certain of its preferred embodiments, it is noted that the embodiments disclosed are illustrative rather than limiting in nature and that a wide range of variations, modifications, changes, and substitutions are contemplated in the foregoing disclosure and, in some instances, some features of the present invention may be employed without a corresponding use of the other features. Many such variations and modifications may be considered desirable by those skilled in the art based upon a review of the foregoing description of preferred embodiments. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.